Drives me mad. DM and MIL especially are fond of this sort of nonsense.
Gems I've had include:
"Put the (newborn) baby to sleep on her tummy" DM
"Oof, why is she still in your room at seven months? OH was moved into his own bedroom at 1 day old, he kept me awake with his snuffling" MIL
"Breastfeeding shouldn't take so long, in my day you got all you needed in the first five minutes on each side. After that it's just comfort" DM
"Don't cuddle DD to sleep. You'll never break that habit" MIL
"You were just left to cry if you were being naughty for bed. I used to wheel you to the bottom of the garden in your pram and shut the door!" DM
"Give DD a rusk, you were all on baby rice at eight weeks" Both
All outdated rubbish, most of which has been proven so by modern science. Worse, some of it dangerous. And, when challenged all followed by the famous "I did it and you were fine", "you're making a rod for your own back" or "all this new advice is rubbish and just an attempt to make money" 
Luckily I'm a confident enough person to tell both of them that I disagree and won't be doing that (whatever it is). They do get mightily offended sometimes!